Neuronal changes of hypokalemic myopathy. A light- and electron-microscopic study on muscle biopsy

Hypokalemic myopathy has been observed in various clinical conditions. There are many studies of the pathomorphological changes of muscle fibers but alterations in intramuscular nerves and motor end-plates are seldom mentioned. The present authors observed biopsied muscle from a 51-year-old housewife who had suffered from gradually increasing muscle weakness. Laboratory examinations revealed a severe hypokalemia of 1.5 mEq/1, 18304 U/1 of CPK, 1300 U/1 of LDH, 343 U/1 of SGOT and 297 IU/1 of adolase. Light-microscopic examination showed changes previously described, including twin-peaked distribution in the histogram of type I, IIA and IIB fibers, ballooning and thickening of terminal axon, and 2 or 3 end-plates closely spaced along the length of muscle fibers. The electron-microscopic examination revealed empty folds of basement membrane in end-plate regions, reduced secondary synaptic clefts, interposition of Schwann cell processes between nerve ending and primary synaptic cleft, and an increase of disarranged microtubules and neurofilaments in terminal axons. The findings suggest that severe hypokalemia primarily produces structural alterations of intramuscular peripheral nerves and motor end-plates as well as of muscle fibers.